The present invention relates to a fuel pump, and particularly to a fuel pump to be installed in a high temperature environment.
With a small outboard motor, as shown in FIG. 4, a fuel tank 40 is arranged internally of the boat, and a fuel pump 42 is arranged externally of the boat. The fuel pump 42 is generally secured directly to a cylinder head cover 46 of an engine 44 in consideration of space and to be driven by power from the engine. Fuel from the fuel pump 42 is introduced into the engine 44 through a carburetor 48.
FIG. 5 shows a conventional fuel pump 42, and FIG. 6 is a sectional view taken on line Axe2x80x94A of FIG. 5. The fuel pump 42 comprises a bottom body portion 50 secured to the cylinder head cover 46, a top body portion 52 mounted thereon, and a cover 54. A piston 56 driven by the engine 44 is set so as to move with a reciprocating motion relative to the bottom body portion 50. A diaphragm assembly 60 having a diaphragm 58 is connected to the piston 56. The top body 52 is provided with a suction valve 62 and the discharge valve 64 which separate top and bottom sections of the top body portion 52, which sections communicate through the suction valve 62 and the discharge valve 64.
The fuel pump 42 is assembled by fixing the bottom body 50, the top body 52 and the cover 54 with the diaphragm 58 held between the bottom body 50 and the top body 52. A seal member 66, such as a gasket, is held between the top body portion 52 and the cover 54. For fixing the bottom body portion 50, the top body portion 52 and the cover 54 together in one step, the bottom body portion 50 is formed with a stepped thread insert hole 68, the top body 52 is formed with a thread insert hole 70, and the cover 54 is formed with an internal threaded hole 72. A bolt 74 is inserted into the threaded insert holes 68, 70 from the bottom body portion 50 side so that the bolt 74 is threadedly engaged with the internally threaded portion 72 of the cover 54. The external thread 74 is tightened to the internal thread portion 72 of the cover 54 whereby the bottom body 50, the top body 52 and the cover 54 are integrally fixed.
The diaphragm 58 is held between the bottom body portion 50 and the top body portion 52 whereby a pump chamber 76 is defined within the top body portion 52 adjacent the diaphragm 58. The seal member 66 is held between the top body 52 and the cover 54 and closes a suction chamber 78 and a discharge chamber 80 which are formed independent of each other within the top body portion 52 above the seal member 66. The suction chamber 78 communicates with the pump chamber 76 through the suction valve 62, and the discharge chamber 80 communicates with the pump chamber 76 through the discharge valve 64.
In the fuel pump 42, when the piston 56 and the diaphragm 58 are moved downward in FIG. 5, the discharge valve 64 is closed and the suction valve 62 is opened so that fuel is introduced into the pump chamber 76 from the suction chamber 78. Next, when the piston 56 and the diaphragm 58 move upward in FIG. 5, the suction valve 62 is closed and the discharge valve 64 is opened so that fuel is moved to the discharge chamber 80 from the pump chamber 76.
For sealing the bottom body portion 50 with the cylinder head cover 46, there is used a thermal setting resin such as a phenol resin (bakelite) which is light weight and heat resistant, and has a high strength. The top body portion 52 and the cover 54 are formed of metal, such as aluminum, by die casting. Aluminum is used for the cover 54 because, in order to provide a tight fit when tightening the diaphragm 58, the top body 52 and the seal member 66 by the external thread 74, the cover 54 with the internally threaded hole 72 is made of metal. Aluminum is used for the top body 52 in order to prevent compressed permanent strain due to the tightening of the bottom body 50 and the cover 54.
However, there has been the drawback that when the top body 52 and the cover 54 are formed of aluminum, a rust-proof treatment is necessary, which treatments increases the cost, and increases the weight.
Preferably, the top body 52 and the cover 54 are made of synthetic resin in consideration of economy and weight. However, when the cover 54 is made of synthetic resin, slack occurs in the threaded engagement by the bolt 74, resulting in a possibility of leakage of fuel. Further, when the top body portion 52 is made of synthetic resin, it is tightened between the bottom body 50 and the cover 54, resulting in a compressed permanent strain. Therefore, the top body 52 and the cover 54 could not be made of synthetic resin.
Further, as shown in FIG. 5, the bolt 74 is inserted through the diaphragm 58 and the seal member 66. Therefore, it has been necessary to increase the size of the diaphragm to extend to a location where the bolt 74 can be inserted through the diaphragm 58 and the seal member 66. Further, it is necessary for the diaphragm 58 and the seal member 66 to be formed with a hole (not shown) through which the bolt 74 is inserted, resulting in a possible breakage of the diaphragm 58 and the seal member 66 from formation of the hole.
The present invention has been made in view of the foregoing and has, as its object to provide a fuel pump which is excellent in heat resistance and salt resistance, which is low in cost and light in weight, and which is free from leakage of fuel.
For achieving the aforementioned object, according to the present invention, there is provided a fuel pump in which a diaphragm is held between a bottom body and a top body, and a seal member is held between the top body and a cover, wherein a thermosetting resin is used for the bottom body, a thermoplastic resin is used for the top body and the cover, with the seal member held between said top body and said cover, and said top body and said bottom body, with said diaphragm therebetween, are fixed together by a fixing means.